MANUAL OF THE GRASSES OF THE UNITED STATES 19 



7b. Inflorescence an exserted open or spikelike panicle. 



8a. Lemmas pubescent on the nerves or callus (except in Triodia 



albescens), the midnerve usually exserted as an awn or mucro. 



Nerves glabrous. Callus densely hairy; lemmas firm; panicle 



large, diffuse 17. REDFIELDIA. 



Nerves hairy at least below, the lateral ones often conspicu- 

 ously so. 



Palea long-ciliate on the upper half 32. TRIPLASIS. 



Palea sometimes villous but not long-ciliate on the upper 



half. Perennials 31. TRIODIA. 



8b. Lemmas not pubescent on the nerves nor callus (the inter- 

 nerves sometimes pubescent) , awnless. 



Glumes longer than the lemmas; lateral nerves of lemma margi- 

 nal, the internerves pubescent 16. DlSSANTHELItJM. 



Glumes shorter than the lemmas; lateral nerves of lemma not 



marginal, the internerves glabrous. 



Lemmas chartaceous; grain large, beaked, at maturity forc- 

 ing the lemma and palea open 15. DIARRHENA. 



Lemmas membranaceous; if firm, the grain neither large nor 



beaked. 

 Spikelets subterete; palea longer than the lemma, bowed 



out below 14. MOLINIA. 



Spikelets compressed; palea not longer than the lemma, not 



bowed out below. 

 Lemmas truncate; spikelets 2-flowered 



13. CATABROSA. 



Lemmas acute or acuminate; spikelets 3- to many- 

 flowered. Rachilla continuous, the paleas persistent 

 after the fall of the lemmas (rachilla disarticulat- 

 ing in Sect. Cataclastos) 12. ERAGROSTIS. 



6b. Lemmas 5- to many-nerved, the nerves sometimes obscure. 



Spikelets with 1 to 4 empty lemmas below the fertile florets; nerves 



obscure; lemmas firm 20. UNIOLA. 



Spikelets with no empty lemmas below the fertile florets; nerves 

 usually prominent; lemmas membranaceous (firm in a few 

 species of Bromus and Festuca). 

 Lemmas flabellate; glumes wanting; inflorescence dense, cylin- 



dric. Low annual 33. ANTHOCHLOA. 



Lemmas not flabellate; glumes present; inflorescence not cylin- 



dric. 

 Lemmas as broad as long, the margins outspread; florets closely 



imbricate, horizontally spreading 11. BRIZA. 



Lemmas longer than broad, the margins clasping the palea; 



florets not horizontally spreading. 

 Callus of florets bearded. 



Lemmas erose at summit, awnless 8. FLUMINEA. 



Lemmas bifid at summit, awned 29. SCHIZACHNE. 



Callus not bearded (lemmas cobwebby at base in Poo). 



Lemmas not erose (slightly in Puccinellid) . 

 9a. Lemmas keeled on the back (somewhat rounded in 



Poa scabrella and its allies) . 



Spikelets strongly compressed, crowded in one-sided 

 clusters at the ends of the stiff, naked panicle 



branches 21. DACTYLIS. 



Spikelets not strongly compressed, not crowded in one- 

 sided clusters. 



Lemmas awned from a minutely bifid apex (awnless 

 or nearly so in Bromus catharticus and B. brizae- 



formis) ; spikelets large 2. BROMUS. 



Lemmas awnless ; spikelets small 10. POA. 



9b. Lemmas rounded on the back (slightly keeled toward 



the summit in Festuca and Bromus). 

 Glumes papery; lemmas firm, strongly nerved, scarious- 

 margined; upper florets sterile, often reduced to a 

 club-shaped rudiment infolded by the broad upper 

 lemmas. Spikelets tawny or purplish, usually not 

 green 28. MELICA. 



